Evaporation of levitating microdroplets containing nanoparticles: luminescent upconverting Gd2O3:Er3+, illumination with 805 nm laser from below via optical fiber, collection with cooled-sensor spectrometer

Microdroplets of suspension were levitated in a linear quadrupole trap and studied similarly as described, e.g. in Y. Shopa et al., JQSRT 296 (2023), but illumination with an 805 nm diode laser (CW, ~1.5 W), which excited luminescence by up-conversion, was provided (vertically) from below via a 200 micrometer-core fiber for circularization. Its polarization was p. In some experiments, the droplet was additionally illuminated with a 515 nm diode laser with p-polarisation. The suspended phase consisted of nanoparticles of Gd2O3:Er3+ or Gd2O3:Nd3+ of several concentrations. The continuous phase consisted of diethylene glycol (2EG). The data is divided into the corresponding folders. In this series of experiments, a grating spectrometer with a cooled sensor was used (Simtrum MC/400-930), which enabled shorter integration times. Two groups of spectral lines were visible (green (stronger) and red). We followed the temporal evolution of several selected lines, both in luminescence and in scattering at right angle (in this series of experiments, usually 515, 523, 538, 550, 554, 560, 563, 630, 654, 661, 682, 805 nm): files *-Spectra.csv, where * (in hh_mm_ss format) always denotes the time of measurement file creation. Simultaneously, the shadow image of the droplet was recorded (non-coherent light, 630 nm LED) - in some cases, a movie: *_Shadow-*.avi is provided. The droplet radius was measured by fitting an ellipse to the shadow edge. The ellipse parameters' temporal evolution is stored in *-Shadow.csv files: time, mean diameter (mean of the ellipse axes), long axis rotation, X and Y of the centre, long and short axis, border length, X and Y of “the centre of mass” of the border, fitting error. The microdroplet's vertical position was stabilised with a DC field. The corresponding voltage variation and other stabilisation system parameters are stored in *.csv files: KeyStab: 0 – stabilisation off, 2 – on, k_PID – proportionality parameter of the software voltage regulator, freq – trapping AC field frequency – usually has no sense in this series of measurements, since it was provided from a manually controlled generator. Time stored in the corresponding files was synchronised. In-focus movies (Images_*.avi, see readme.txt for details) of the evaporating microdroplet were recorded for certain experiments to illustrate its evolution – no synchronisation is available. It must be kept in mind that the observed image is, for the most part laser speckle. The "Laser on/off" pertains to the 805 nm laser. Further details can be found in the readme.txt files in the corresponding folder. (No)_th_spectrum.csv represents the ith recorded spectrum from the corresponding experiment. The parameters of the Gd2O3:Er3+ samples can be found in the .ppt file.将悬浮液微滴束缚于线性四极阱（linear quadrupole trap）中，实验方案参照Y. Shopa等人发表于JQSRT 296 (2023)的研究开展，但本实验采用805 nm连续波（CW，约1.5 W）二极管激光器进行照明：该激光器通过上转换发光（up-conversion luminescence）激发样品荧光，经由芯径200微米的光纤从下方垂直入射以实现光路圆形化，入射偏振为p偏振。部分实验中，额外采用515 nm p偏振二极管激光器对微滴进行照明。 悬浮相由不同浓度的Gd₂O₃:Er³⁺或Gd₂O₃:Nd³⁺纳米颗粒构成，连续相则为二甘醇（diethylene glycol, 2EG）。数据集按对应实验分组存放于不同文件夹中。 本系列实验采用搭载制冷传感器的光栅光谱仪（grating spectrometer，型号Simtrum MC/400-930），可实现更短的积分时长。实验中观测到两组特征谱线：绿光波段（强度更高）与红光波段。我们追踪了多条选定谱线的时间演化特性，涵盖发光与直角散射信号，本系列实验所选波长通常为515、523、538、550、554、560、563、630、654、661、682、805 nm：相关光谱数据存储于格式为*-Spectra.csv的文件中，其中*以hh_mm_ss格式表示对应测量文件的创建时刻。 同时记录了微滴的阴影图像（采用630 nm LED非相干光照明），部分实验还同步录制了视频文件，格式为*_Shadow-*.avi。微滴半径通过对阴影边缘进行椭圆拟合得到，椭圆参数的时间演化数据存储于*-Shadow.csv文件中，包含以下字段：测量时刻、平均直径（椭圆两轴的平均值）、长轴旋转角、中心坐标(X,Y)、长轴与短轴长度、边界长度、边界的质心坐标(X,Y)以及拟合误差。 微滴的竖直位置通过直流电场（DC field）实现稳定，对应的电压调控数据及其他稳定系统参数存储于*.csv文件中，其中KeyStab字段用于标识稳定状态：0代表未开启稳定，2代表开启稳定；k_PID为软件电压调节器（software voltage regulator）的比例参数；freq为捕获交流电场频率——本系列测量中该参数无实际意义，因捕获电场由手动控制的信号源提供。所有对应文件中的时间戳均已完成同步。 部分实验录制了蒸发微滴的焦平面视频（文件格式为Images_*.avi，详细说明参见readme.txt），用于展示微滴的演化过程，该视频未参与时间同步。需注意：观测到的图像主体为激光散斑（laser speckle）。文中提及的“激光器启停（Laser on/off）”特指805 nm激光器的工作状态。更多细节可查阅对应文件夹中的readme.txt文件。(No)_th_spectrum.csv 代表对应实验中第i条记录的光谱。Gd₂O₃:Er³⁺样品的相关参数可从对应文件夹内的.ppt文件中获取。